Combustion chamber of an internal combustion engine

ABSTRACT

An internal combustion engine comprising a first raised portion formed on the inner wall of the cylinder head, a second raised portion formed on the top face of the piston at a position opposite to the first raised portion with respect to the axis of the piston, and a third raised portion formed on the inner wall of the cylinder head above the second raised portion. A first flat squish area is formed between the flat peripheral top face of the piston and flat bottom face of the first raised portion. A second spherical shell shaped squish area is formed between the spherical bottom wall of the third raised portion and the spherical rear face of the second raised portion. A pair of spark plugs is arranged on the top face of the combustion chamber. One of the spark plugs is arranged in the vicinity of said first raised portion, and the other spark plug is arranged in the vicinity of said third raised portion.

DESCRIPTION OF THE INVENTION

The present invention relates to a construction of the combustionchamber of an internal combustion engine.

As a method of simultaneously reducing the amount of harmful HC, CO andNO_(x) components in the exhaust gas, a method of using a lean air-fuelmixture has been used. In addition, as a method of reducing the amountof harmful NO_(x) components in the exhaust gas, a method of using amixture containing the recirculated exhaust gas therein has been used.However, either when a lean air-fuel mixture is used or when a mixturecontaining the recirculated exhaust gas therein is used, a problemoccurs in that, since the flame speed of either mixture is very low andthe burning velocity is thus low, a stable combustion cannot beobtained. In order to obtain a stable combustion by using a leanair-fuel mixture or a mixture containing the recirculated exhaust gastherein, it is necessary to increase the burning velocity. As ofincreasing the burning velocity, a method creation of a strongturbulence in the combustion chamber can be used. As an engine which iscapable of increasing the burning velocity by creating a turbulence inthe combustion chamber, the inventor has proposed an engine whichcomprises a first downwardly projecting raised portion formed on theperiphery of the inner wall of the cylinder head and having a flatbottom face so as to form a first squish area between the flat bottomface of the first raised portion and a flat peripheral portion of thetop face of the piston when the piston approaches the top dead center.In addition, this engine further comprises a second upwardly projectingraised portion formed on the top face of the piston at a positionopposite to the flat peripheral portion of the top face of the pistonwith respect to the axis of the cylinder so as to form a second squisharea between the inner wall of the cylinder head and the rear face ofthe second raised portion when the piston approaches the top deadcenter. In addition, in this engine, the second raised portion has aninclined front face which is exposed to the combustion chamber andsmoothly connected to the flat peripheral portion of the piston. At theend of the compression stroke, a swirl motion rotating about thehorizontal axis is created in the combustion chamber by the pair ofsquish flows spouted from the first and the second squish areas,respectively, in the combustion chamber.

In the above-mentioned engine, since a swirl motion rotating about thehorizontal axis is created in the combustion chamber, it is true thatthe burning velocity can be increased as compared with that in aconventional engine. However, in the above-mentioned engine, asatisfactorily high burning velocity cannot be obtained and, thus, it isnecessary to obtain a more stable combustion and improve the specificfuel consumption by further increasing the burning velocity.

An object of the present invention is to provide an internal combustionengine capable of considerably increasing the burning velocity bycreating a considerably strong swirl motion in the combustion chamberand by arranging a pair of ignition sources in the combustion chamber atpositions spaced from each other.

According to the present invention, there is provided an internalcombustion engine comprising: a cylinder block having a cylinder boretherein; a cylinder head mounted on the cylinder block and having aninner wall; a first raised portion having on its lower end a flat bottomface and being formed on the periphery of the inner wall of the cylinderhead so as to project downwards; a piston reciprocally movable in thecylinder bore and having a top face which has a flat peripheral portionapproachable to the flat bottom face so as to create a first squish areatherebetween at the end of the compression stroke for spouting out afirst squish flow along the top face of the piston, the inner wall ofthe cylinder head and the top face of the piston defining a combustionchamber therebetween; an intake valve movably mounted on the cylinderhead for guiding a combustible mixture into the combustion chamber; anexhaust valve movably mounted on the cylinder head for dischargingexhaust gas into the atmosphere, and; a second raised portion formed onthe top face of the piston at a position opposite to the first raisedportion with respect to an axis of the piston and having a rear face anda front face exposed to the combustion chamber, the rear face beingapproachable to the inner wall of the cylinder head so as to create asecond squish area therebetween at the end of the compression stroke forspouting out a second squish flow which moves forwards in the upperinterior of the combustion chamber in the direction opposite to thespouting direction of the first squish flow, the first and second squishflows cooperating with each other to create a strong swirl motionrotating about a horizontal axis in the combustion chamber, wherein theimprovement comprises a third raised portion formed on the inner wall ofthe cylinder head above the second raised portion and having a bottomwall which cooperates with the rear face of the second raised portionfor creating the second squish area therebetween, and a pair of sparkplug arranged in the combustion chamber at positions spaced from eachother.

The present invention may be more fully understood from the descriptionof a preferred embodiment of the invention set forth below, togetherwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of an internal combustion engineaccording to the present invention;

FIG. 2 is a bottom view taken along the line II--II in FIG. 1;

FIG. 3 is a cross-sectional side view taken along the line III--III inFIG. 1, and;

FIG. 4 is a perspective view of the piston illustrated in FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIGS. 1 through 3, 1 designates a cylinder block, 2 apiston reciprocally movable in the cylinder block 1, 3 a cylinder headfixed onto the cylinder block 1 via a gasket 4 and 5 a combustionchamber formed between the top face of the piston 2 and the inner wallof the cylinder head 3. 6 designates an intake valve, 7 an intake port,8 an exhaust valve, 9 an exhaust port, and 10 and 11 spark plugs. As isillustrated in FIGS. 1 through 3, the inner wall of the cylinder head 3has an annular flat surface 12 which extends circumferentially over theentire periphery of the inner wall of the cylinder head. The flatsurface portion 12a of the annular flat surface 12, which is located onthe left side in FIG. 2, has a uniform width illustrated by the arrow Ain FIG. 2, while flat surface portions 12b and 12c of the annular flatsurface 12, which are located on the right side in FIG. 2, have widthswhich are wider than the width A of the flat surface portion 12a asillustrated by the arrows B and C in FIG. 2, respectively. In addition,from FIG. 2, it will be understood that the flat surface portion 12blocated near the exhaust valve 8 has width B which is wider than width Cof the flat surface portion 12c located near the intake valve 6. As isillustrated in FIGS. 1, 3 and 4, an annular flat surface 13 arranged toface the annular flat surface 12 of the cylinder head 3 and having ashape which is approximately equal to that of the annular flat surface12 is formed on the top face of the piston 2. That is, the flat surfaceportion 13a of the annular flat surface 13, which is formed on the topface of the piston 2 so as to face the flat surface portion 12a of thecylinder head 3, has a uniform width which is approximately equal to thewidth A of the annular flat surface 12, and the flat surface portions13b and 13c of the annular flat surface 13, which are formed on the topface of the piston 2 so as to face the flat surface portions 12b and12c, respectively, have widths which are wider than the width of theflat surface portion 13a of the piston 2. Consequently, when the piston2 is positioned at the top dead center as illustrated in FIG. 1, a flatand annular squish area S is formed between the annular flat surface 12of the cylinder head 3 and the annular flat surface 13 of the piston 2.As illustrated in FIGS. 1 and 3, the top face 14 of the combustionchamber 5 has a spherical shape; in addition, the side wall 15 of thecombustion chamber 5 extends approximately vertically from the flatsurface portions 12b, 12c of the cylinder head 3 to the top face 14 ofthe combustion chamber 5. A downwardly projecting raised portion 16 isformed on the top face 14 at a position opposite to the spark plug 10with respect to the axis of the piston 2, and the bottom wall 16a of theraised portion 16 has a spherical shape. The lower edge of the bottomwall 16a of the raised portion 16 is connected to the flat surfaceportion 12a of the cylinder head 3, and the upper edge of the bottomwall 16a is connected to the top face 14 of the combustion chamber 5 viaa steeply inclined side wall 16b arranged to be exposed to thecombustion chamber 5. As illustrated in FIG. 1, the electrode of thespark plug 11 is arranged on the top face 14 of the combustion chamber 5at a position near the steeply inclined side wall 16b of the raisedportion 16. A raised portion 17 is formed on the top face of the piston2 at a position opposite to the flat surface portions 13b, 13c of thepiston with respect to the axis of the piston 2, and the rear face 18 ofthe raised portion 17 has a spherical shape complementary to the shapeof the bottom wall 16a of the raised portion 16. In addition, the loweredge of the rear face 18 of the raised portion 17 is connected to theflat surface portion 13a of the piston 2. Consequently, when the piston2 is positioned at the top dead center as illustrated in FIG. 1, aspherical shell shape squish area T is formed between the bottom wall16a of the raised portion 16 and the rear face 18 of the raised portion17. In addition, a flat and shallow depression 19 is formed in thecentral portion of the top face of the piston 2 at a position locatedinside of the flat surface portions 13b, 13c of the piston 2, and theraised portion 17 has an inclined front face 20 extending from the flatdepression 19 to a ridge 21 of the raised portion 17 and arranged to beexposed to the combustion chamber 5. As is illustrated in FIG. 1, theridge 21 of the raised portion 17 is rounded. As can be seen in FIGS. 2and 4, the first annular squish area extends inwardly from the peripheryof the top face of the piston to a continuous, sinuous inner peripherywhich extends around and is almost vertically under the intake valve 6,exhaust valve 8, and spark plug recess 22. The first squish area isadjacent to the second raised portion 17. Recess 22 extends outwardlybeyond a straight line extending between the peripheries of the intakevalve 6 and exhaust valve 8. As is illustrated in FIGS. 1 through 3, asemi-cylindrical recess 22, which has a particular shape wherein thelower end of the semi-cylinder is obliquely cut, is formed on the topface 14 of the combustion chamber 5 at a position opposite to the squisharea T with respect to the axis of the piston 2, and the electrode ofthe spark plug 10 is arranged in the recess 22. Consequently, theelectrode of the spark plug 10 is partially enclosed by a verticallyextending semi-cylindrical wall 23. As mentioned hereinafter, when thepiston 2 approaches the top dead center, a pair of squish flows shown bythe arrows F and G in FIG. 1 is spouted from the squish areas S and T,respectively, and the electrode of the spark plug 10 is arranged on anextension of the squish area T so that the squish flow G impingesdirectly upon the electrode of the spark plug 10. However, it should benoted that, when the downward movement of the piston 2 is started, apair of gas streams flowing towards the squish areas S and T indirections which are opposite to those of the squish flows G and F,respectively, is created in the combustion chamber 5.

During operation, at the time of the intake stroke, when the downwardmovement of the piston 2 is started, the pair of gas streams flowingtowards the squish areas S and T at a high speed in directions which areopposite to those of the squish flows G and F, respectively, is createdin the combustion chamber 5 due to the temporary pressure drop withinthe squish areas S and T, and a strong turbulence is thus created in thecombustion chamber 5. As a result of this, the air-fuel ratio of a leanmixture or a mixture containing the recirculated exhaust gas therein inthe combustion chamber 5 becomes uniform over the entire region of thecombustion chamber 5. When the mixture contains recirculated exhaustgas, the air-fuel mixture is completely mixed with the recirculatedexhaust gas due to the above-mentioned strong turbulence. After this, atthe time of the compression stroke, when the piston 2 approaches the topdead center, the squish flows F and G are spouted from the squish areasS and T, respectively. The squish flow F spouted from the squish area Sflows towards the front face 20 of the raised portion 17, and the squishflow G spouted from the squish area T moves forward towards the recess22. Then, the squish flow G impinges upon the semi-cylindrical wall 23,and a microturbulence is thus created in the recess 22. On the otherhand, the squish flow F flowing towards the front face 20 of the raisedportion 17 from the squish area 5 moves forward along the front face 20of the raised portion 17 and then comes into violent contact with thesquish flow G spouted from the squish area T. As a result of thisviolent contact, the flow direction of the squish flow G is changed sothat the squish flow G flows along the top face 14 of the combustionchamber 5 as illustrated by the arrow H in FIG. 1. At this time, sincethe flow direction of the squish flow F is changed by the steeplyinclined side wall 16b of the raised portion 16, the squish flow F alsoflows along the top face 14 of the combustion chamber 5 as illustratedby the arrow H in FIG. 1. By forming the steeply inclined side wall 16bwhich extends upwards from the ridge 21 of the raised portion 17, thesquish flow G is not considerably decelerated by the squish flow F, andthe squish flow F itself is also not considerably decelerated. Then, thesquish flow H flowing along the top face 14 of the combustion chamber 5passes in front of the recess 22 and moves downwards along the verticalside wall 15. At this time, since the electrode 11 of the spark plug 10is arranged within the recess 22, the squish flow H does not impingedirectly upon the electrode 11 of the spark plug 10. Then, the squishflow H flowing downwardly along the vertical side wall 15 comes intoviolent contact with the squish flow F spouted from the squish area S;as a result, the flow direction of the squish flow F is changed asillustrated by the arrow I in FIG. 1. At this time, the squish flow Galso flows along the flat bottom of the depression 19 as illustrated bythe arrow I in FIG. 1. By forming the depression 19 in the top face ofthe piston 2, the squish flow F is not considerably decelerated by thesquish flow H, and the squish flow F is also not considerablydecelerated. Thus, a strong swirl motion, shown by the arrow K, rotatingabout the horizontal axis is created in the combustion chamber 5.

Then, the mixture is ignited by the spark plugs 10 and 11 at the sametime. At this time, since a microturbulence is created in the recess 22as mentioned previously, the mixture is easily ignited and then theflame rapidly spreads within the recess 22. On the other hand, asmentioned previously, the flow direction of the squish flow G spoutedfrom the squish area T is changed by the squish flow F and, as a result,the squish flow G is caused to flow along the steeply inclined side wall16b of the raised portion 16. At this time, a strong turbulence iscreated on the top face 14 of the combustion chamber 5 at a positionnear the steeply inclined side wall 16b by the squish flows G and F. Asa result, the mixture is easily ignited by the spark plug 11. When thespark plug 11 is so arranged that the electrode thereof projects intothe combustion chamber 5 to a great extent, since the squish flow Gimpinges directly upon the electrode of the spark plug 11, there is adanger that the flame formed on the electrode of the spark plug 11 willbe extinguished. Consequently, it is preferable that the electrode ofthe spark plug 11 be arranged at a position as close as possible to thesteeply inclined side wall 16b and the top face 14. In the case whereinthe flame formed on the electrode of the spark plug 11 is extinguishedeven if the electrode of the spark plug 11 is arranged at a positionclose to the steeply inclined side wall 16b and the top face 14, it isnecessary to form a recess on the top face 14 of the combustion chamber5 and position the electrode of the spark plug 11 within that recess.

The flames formed around the spark plugs 10 and 11, which are arrangedto be spaced from each other, swirl in the combustion chamber 5 togetherwith the strong swirl motion K and the burning velocity is thusconsiderably increased. In addition, since the flame swirls in thecombustion chamber 5, unburnt HC and CO located in the quench layersformed on the inner wall of the cylinder head 3 and on the top face ofthe piston 2 are burned. After this, when the downward movement of thepiston 2 is started, the unburnt gas in the combustion chamber 5 issucked into the squish areas S and T together with the flame. As aresult, the unburnt HC and CO located in the quench layers formed on theinner wall of the cylinder head 3 and on the top face of the piston 2within the squish areas S and T are burned. As is illustrated in FIG. 1,in the present invention, the spark plug 11 is arranged in the vicinityof the squish area T. Consequently, when the downward movement of thepiston 2 is started, since the flame formed around the spark plug 11 issucked into the squish area T together with the unburnt HC and CO, theunburnt HC and CO sucked into the squish area T is immediately burnedand, as a result, the burning velocity is considerably increased.However, in the case wherein the flame formed around the spark plug 11is sucked into the squish area T as mentioned above, there is a dangerthat, when the engine is operating under a heavy load, the selfignitionof the unburnt gas located at the peripheral end of the squish area Twill be caused and, as a result, knocking will occur. Therefore, inorder to prevent knocking from occurring, it is preferable that theigniting operation of the spark plug 11 remain stopped when the engineis operating under a heavy load.

In an internal combustion engine having such a construction that a swirlmotion is created in the combustion chamber by the squish flow, thestrength of the squish flow has a great influence on the strength of theswirl motion. In addition, the surface area of the squish area has agreat influence on the strength of the squish flow. However, it isimpossible to increase the surface area of the squish flow to a greatextent in view of the construction of an engine. In addition, in thecase wherein an excessively strong swirl motion is created in thecombustion chamber, there is a danger in that a misfire will occur. As aresult of experiments conducted by the inventor, in the engineillustrated in FIGS. 1 through 4, it has been proven that, in order toobtain an ease of ignition and a good combustion, it is preferable thata surface area ratio of the sum of the squish area formed on the innerwall of the cylinder head 3 and the squish area formed on the top faceof the piston 2 to the sum of the cross-sectional area of the cylinderbore and the surface area of the inner wall of the cylinder head 3,except for the surface area of the vertical side wall 15, be in therange of 30 percent to 50 percent. In addition, it has also been proventhat the best ignition and combustion can be obtained when theabove-mentioned surface area ratio is in the range of 35 percent to 40percent. In the present invention, in order to form squish areas S and Thaving a large surface area while forming the combustion chamber 5 ascompact as possible, the squish area S must be so formed that it has anannular shape.

In addition, as mentioned previously, since the flat surface portion 12bof the cylinder head 3 has the width B which is wider than the width Cof the flat surface portion 12c of the cylinder head 3, the squish flowspouted from the flat surface portion 12b as illustrated by the arrow Fbin FIG. 2 is stronger than that spouted from the flat surface portion12c as illustrated by the arrow Fc in FIG. 2. In addition, as isillustrated by the broken lines Tb, Tc in FIG. 2, the squish area T isso formed that the surface area of the squish area portion Tb locatednear the exhaust valve 8 is considerably greater than that of the squisharea portion Tc located near the intake valve 6; as a result, the squishflow Gb spouted from the squish area portion Tb is stronger than thesquish flow Gc spouted from the squish area portion Tc. Consequently, aswirl motion which rotates about the horizontal axis and which iscreated in the combustion chamber 5 beneath the exhaust valve 8 by thepair of squish flows Fb, Gb becomes stronger than a swirl motion whichrotates about the horizontal axis and which is created in the combustionchamber 5 beneath the intake valve 6 by the pair of squish flows Fc, Gc.As is known to those skilled in the art, knocking occurs due to the factthat the self-ignition of the mixture located near the exhaust valve 8is caused. However, by creating a strong swirl motion in the combustionchamber 5 beneath the exhaust valve 8 and causing the flame of themixture ignited by the spark plug 10 to propagate immediately towardsthe space around the exhaust valve 8, it is possible to prevent knockingfrom occurring.

According to the present invention, since an optimum and strong swirlmotion can be created in the combustion chamber and, in addition, a pairof ignition sources is arranged so as to be spaced from each other inthe combustion chamber, the burning velocity can be considerablyincreased. As a result, a stable combustion can be obtained, and thespecific fuel consumption can be improved.

While the invention has been described with reference to a specificembodiment chosen for purposes of illustration, it should be apparentthat numerous modifications can be made thereto by those skilled in theart without departing from the spirit and scope of the invention.

What is claimed is:
 1. An internal combustion engine comprising:acylinder block having a cylinder bore therein; a cylinder head having aninner wall mounted on said cylinder block; a first raised portion formedon the periphery of the inner wall of said cylinder head, having a flatbottom face and projecting downwardly; a piston reciprocally movable insaid cylinder bore and having a top face with a flat peripheral portionapproachable to said flat bottom face, creating a first squish areatherebetween at the end of the compression stroke for spouting out afirst squish flow along the top face of said piston, said first squisharea comprising an annular area between the flat peripheral portion ofthe top face of the piston and the flat bottom face of the cylinderhead, said first squish area extending substantially along the entireperiphery of the top face of said piston; a combustion chamber definedby the inner wall of the cylinder head and the top face of said piston;an intake valve movably mounted on said cylinder head in fluidcommunication with said combustion chamber; an exhaust valve movablymounted on said cylinder head in fluid communication with saidcombustion chamber; a second raised portion formed on the top face ofsaid piston at a position opposite to said first raised portion withrespect to an axis of said piston, having a rear face and a front faceexposed to said combustion chamber, said rear face being approachable tothe inner wall of said cylinder head so as to create a second squisharea therebetween at the end of compression stroke for spouting out asecond squish flow which moves forward in the upper interior of saidcombustion chamber in a direction opposite to the spouting direction ofsaid first squish flow, said first and second squish flows cooperatingwith each other to create a strong swirl motion rotating about ahorizontal axis in said combustion chamber; a third raised portionformed on the inner wall of said cylinder head above said second raisedportion having a bottom wall which cooperates with said rear face ofsaid second raised portion for creating said second squish area; and apair of spark plugs located in said combustion chamber, comprising afirst spark plug located near said first raised portion in a recessformed on the inner wall of said combustion chamber, said recess beinglocated on an extension of said second squish area and extendingoutwardly beyond a straight line extending between the peripheries ofsaid intake and exhaust valves, and a second spark plug located nearsaid third raised portion, said first squish area extending inwardlyfrom the periphery of the top face of the piston to a continuous,sinuous inner periphery which extends around and is almost verticallyunder the intake valve, the exhaust valve, and said spark plug recessand adjacent to said second raised portion, the surface area ratio ofthe sum of the first and second squish areas formed on the inner wall ofthe cylinder head and the first and second squish areas formed on thetop face of the piston to the sum of the cross-sectional area of thecylinder bore and the surface area of the inner wall of the cylinderhead, excluding the surface area of the vertical side wall of said firstraised portion, is in the range of from 30 to 50 percent.
 2. An internalcombustion engine as claimed in claim 1, wherein said recess has avertically extending semi-cylindrical wall arranged on said extension ofsaid second squish area.
 3. An internal combustion engine as claimed inclaim 1, wherein said combustion chamber has a spherical top face, saidrecess being formed on said spherical top face.
 4. An internalcombustion engine as claimed in claim 1, wherein said second spark plughas a spark gap arranged above the extension plane of said second squisharea.
 5. An internal combustion engine as claimed in claim 1, whereinsaid surface area ratio is in the range of 35 percent to 40 percent. 6.An internal combustion engine as claimed in claim 1, wherein the surfacearea of said first and second squish areas located near said exhaustvalve is larger than that of said first and second squish areas locatednear said intake valve.
 7. An internal combustion engine as claimed inclaim 1, wherein said bottom wall of said third raised portion has aspherical shape, said rear face of said second raised portion having ashape which is complementary to the shape of said spherical bottom wallfor creating a spherical shell shaped squish area between said rear faceand said spherical bottom wall.
 8. An internal combustion engine asclaimed in claim 7, wherein said third raised portion has a steeplyinclined side wall extending upwards from a ridge of said second raisedportion.
 9. An internal combustion engine as claimed in claim 1, whereinsaid first raised portion has a horizontally flat bottom face and anapproximately vertical side wall exposed to said combustion chamber,said first squish area extending in a horizontal plane.
 10. An internalcombustion engine as claimed in claim 9, wherein a depression is formedon the top face of said piston and has an approximately verticalperipheral wall extending downwards from a lower edge of the verticalside wall of said first raised portion.
 11. An internal combustionengine as claimed in claim 10, wherein the front face of said secondraised portion is smoothly connected to a bottom wall of saiddepression.
 12. An internal combustion engine as claimed in claim 11,wherein said front face of said second raised portion is formed so as tobe flat.